It is well known that vinyl chloride monomer (VCM) can be produced from 1,2-dichloroethane (commercially called ethylene dichloride or EDC) by splitting off a molecule of hydrogen chloride. The dehydrohalogenation reaction (commonly called "cracking" in the trade) is typically accomplished by heating the EDC, in the absence of a catalyst, in an inert atmosphere using high temperature and pressure; usually about 550.degree. C. and at a pressure of about 300 to 600 psi (21-42 Kilograms/centimeter.sup.2 ; 2,070,000 to 4,140,000 Pascals).
A serious disadvantage of the standard Pyrolysis or thermal process is the need of a large amount of costly heat energy to accomplish the cracking. Another serious difficulty encountered in such a process is the rapid deposition of solid by-products (coke) on the tubes which limits the process to relatively short operating periods before cleaning of the tubes is required. Lastly, in these high temperature processes, undesirable side reactions frequently occur which lower the conversion of EDC.
To reduce the problems observed in the standard pyrolytic cracking process various catalytic processes have been proposed. For example, U.S. Pat. No. 2,877,277 teaches the use of an alkaline earth metal hydroxide in aqueous solution to promote the dehydrochlorination of EDC to VCM, and refers to the prior use of alkali metal hydroxides. These processes suffer from the disadvantages of a very long contact time (30 minutes to 2.5 hours) and difficulty in the separation and purification of the resultant VCM from the aqueous solution.
U.S. Pat. No. 3,290,399 teaches the use of graphite to promote the cracking reaction, and references the use of activated carbon washed with nitric acid as disclosed in British Patent No. 823,285. The processes suffer in that reaction temperatures and pressures are still high, up to 600.degree. C.
Japanese Patent No. 24870/64 teaches the use of a catalyst of a boron compound such as boric acid on activated charcoal.
Lastly, U.S. Pat. No. 3,896,182 teaches that the clogging of Pyrolysis reactor tubes by carbonaceous substances (coking) can be reduced by conducting the reaction in the substantial absence of oxygen, below 2.0 ppm of oxygen present.
While such processes may be commercially feasible, there has been and still is a continuing search for catalytic materials which will improve the dehydrohalogenation process by enabling the use of lower operating temperatures and pressures and further reduction in undesirable side reactions and coking.